1. Field of the Invention
The present invention relates generally to a method and a system for generating tool path data for an automatic machining center through a three-dimensionally curved plane. More specifically, the invention relates to a method and a system for deriving numerical data for defining the automatic machining center in a numerically controlled (NC) machine.
2. Description of the Background Art
Recently, computerized automatic drafting (CAD) systems and computerized automatic machining (CAM) center systems have been developed. In addition, in order to provide for the automatic planning of the center of a three-dimensionally curved plane and for controlling an automatic machining tool, CAD/CAM systems have been developed.
Conventionally, automatically programmed tools (APT) are known for establishing tool paths. APT is programmed utilizing a general purpose automatic programming language for multi-axes surface control, which language has generally an equivalent structure to English. Such a language to be used for APT includes instructions, definitions and so forth for geometrical configurations of the work and the tool, kinematic action of the tool relative to the work, performance of the machine, tolerances, arithmetic operations and so forth. By applying a program generated by the APT language to a large computer, an NC tape can be obtained.
On the other hand, when the data description of the external dimensions and a curved surface are to be processed in the computer, a parametric description type system, such as a Bezier system or a B-Spline system is frequently used.
A fundamental and essential problem which arises in establishing the tool path, is the derivation of data in consideration of the machining accuracy and interference of the tool.
In the aforementioned APT, the user programs the tool path and, as a result, machining data is established for the curved surface. That is, the machining data cannot be automatically established from a geometrical model. Fundamentally, the high efficiency in a CAD/CAM system comes from transferring of design data in planning to machining. Therefore, APT is inefficient since designing and programming of the tool path are performed separately and irrespective of each other.
A curved surface described by parametric type data is advantageous in defining the configuration of the surface by not relying on a coordinate system. However, since the NC machines for machining curved surfaces are controlled by a coordinate system, accurate conversion from the curved surface data derived in the computer into machining data is not possible. Thus, machining accuracy cannot be obtained. Also, when the data describes the product in a parametric manner, it is technically impossible to check for interference or collision of the tool and/or tool holder prior to finishing the configuration of the work. As a result, necessary sections tend to be cut inadvertently.
There are other processes for describing polyhedrons equivalent to a curved surface, however, high machining accuracy cannot be expected unless an extraordinarily large volume of data is processed. This requires an unacceptably long period for processing the data for a practical application for an NC machine. On the other hand, in order to shorten the process period, the volume of data has to be reduced, which lowers the machining accuracy.